The present invention relates to Global Navigation Satellite System (GNSS) receivers, and more particularly, to a method and apparatus for reducing Time To First Fix (TTFF) of a GNSS receiver without accurate time information.
One of the most important issues related to GNSS receivers is how to obtain accurate GNSS time when a GNSS receiver enters a start-up mode from a power-off mode. Typically, within a conventional GNSS receiver, all components except a real time clock (RTC) are powered down in the power-off mode. According to the related art, a common way to get an initial GNSS time when the GNSS receiver is powered on is by reading the RTC time from the RTC and by performing further calculations. After deriving the initial GNSS time for the start-up mode, some initialization operations may be performed accordingly. Whether the initial GNSS time is accurate or not may influence the TTFF of the GNSS receiver.
As most operations before the TTFF of the conventional GNSS receiver (e.g. the initialization operations mentioned above) are based on the RTC, the RTC has become an essential component of the conventional GNSS receiver. As a result, any damage or power failure of the RTC will certainly cause malfunction or lower performance of the GNSS receiver implemented according to the related art. In addition, the corresponding material costs of the RTC will always be included in the overall cost list of the manufacturer.
Additionally, a button battery is typically required for powering the RTC during the power-off mode. The button battery is harmful to the environment, however, causing the conventional GNSS receiver to be environmentally-unfriendly. Some end users may feel ashamed of having yet another environmentally-unfriendly product like this.